The present invention relates generally to the field of reclaiming and utilizing waste carbonaceous materials. More specifically, the invention relates to coal additive emulsions.
Coal is used as an energy source in many industrial settings. Regrettably, there are many problems that accompany the industrial use of coal to generate heat. These problems arise during mining, preparation prior to shipping, storage, preparation prior to use and the use of coal.
The mining of coal gives rise to the first of these problems. Typically, after handling and cleaning is completed, about 15-20% of the coal mined consists of fines ranging in size from powder to small granules. For the most part, these fines are not directly usable, thereby leaving great quantities of material that is wasted and represents a hazardous and expensive disposal problem. Typically, coal fines are disposed of at or near the mine site in unsightly piles, trenches or ponds. The fines material from mining operations are frequently recovered in the form of a wet filter containing about 20-30% moisture, depending upon its size, distribution and ash content. Currently, there are over two billion tons of discarded coal fines throughout the United States. While a portion of the coal fines can be combined with coarser fractions of mine production for sale, the inclusion of all fines often reduces the quality of the product below market requirements. Accordingly, coal fines handling, storage and disposal operations represent a significant and unproductive expense for the industry.
The next problem that contributes to the underutilization of coal fines for conventional uses is their relatively high moisture content after processing in coal preparation plants. The heating value of coal is reduced as its moisture content increases. Since the value of coal depends on its heating value, it follows that the price can be increased by reducing the moisture content. Therefore, the coal industry typically reduces the moisture in coal prior to shipment to utilities and industrial customers in order to increase its heating value and price. This reduction in moisture increases the efficiency of power plants and decreases transportation costs. The process of reducing coal moisture, though, further contributes to the problem of coal fines production because as water is removed, the coal structure is weakened leading to the production of further coal particles. Thus, coal drying operations are yet another source of fines.
Once mined, prepared and shipped, the coal is typically stored prior to use. During storage two other problems arise. First, the coal that had been expensively reduced in water content by drying now sits and absorbs ambient water. This, as explained above, lowers its BTU value. Second, the dry coal is brittle and fines that contribute to coal dust problems are produced. These dust problems are a nuisance to neighbors and may, in some cases, violate local fugitive dust emission regulations.
In some cases the coal is transformed into coke prior to use. Coke is essentially a high carbon content, component used primarily in steel making, blast furnaces and other industrial applications. It is made from metallurgical grade coal that is heated anaerobically in large ovens. The volatile matter is driven off, leaving fixed carbon and leading to the flaking off of coal fines. As such, the coke making process is yet another source of coal fines.
Lastly, heating coal in furnaces gives rise to two important environmental concerns, sulfur and ash. Coal that is high in sulfur cannot be used efficiently as a fuel source because regulations prohibit sulfur stack emissions. Coal that produces a high ash content cannot efficiently be used either due to regulations prohibiting particulate matter emissions. These regulations are commonly referred to as pm-2.5. This is particulate matter above 2.5 nanometers in size. This particulate matter contributes to visibility problems and is thought to be the cause of the recent alarming increase in the incidence of asthma. The visibility problems are recognized where the opacity of the stack plume is high, in that it is less transparent. Ash is such a problem that a large body of research has been devoted to additives that aid complete combustion without ash production. These chemical additives have been added with feedstock fuel but, problems regarding consistent levels of additives have remained an issue.
As a result of these problems, as well as the strict customer quality demands and stringent regulation of mine waste disposal practices to satisfy environmental standards, coal fine utilization has been recently reexamined by the industry. In the past, fines have been used mostly for manufacture and briquettes for home and commercial heating. Coal briquetting technology focused on low-pressure agglomeration of coal fines, using a binder, typically of coal tar origin, to hold individual particles together. This technology flourished during the early part of the century, when coal briquette products were utilized as home heating fuel, but this application has essentially disappeared since the end of World War II due to a shift to other more convenient sources of fuel. Therefore, this opportunity for commercial utilization of coal fines has been drastically reduced.
Recently, as the amount of available landfill space dwindles, disposal costs have risen, thus increasing public pressure to find alternatives to land fills for waste coal products. As land fill costs rise the economics of using waste as fuel has become more favorable. Not only does the use of waste as a fuel save disposal costs, but often these wastes are closer to potential customers than are sources of raw coal, thus reducing transportation costs.
In spite of the desirability to reclaim coal waste for fuel, the small size of coal fines presents a significant problem when they are used industrially. In a dry state, the fines are generally predominantly passable through a 28 mesh screen. Industrial coal furnaces generate a high velocity vortex as heat rises through the exhaust stack. When fine particles enter this vortex they are simply carried up the exhaust stack. By being carried up the exhaust stack the energy value of the coal is not utilized and the particles contribute further to the problem of particulate matter emissions. Also the use of unbound fines is unpredictable. This unpredictability prohibits a furnace operator from uniformly feeding the furnace so the furnace can operate in an efficient manner. Therefore, to be useful to industry, the fines must be uniformly agglomerated in some way.
One approach has been to design specialized boilers to burn the specified waste. Unfortunately, such specialized boilers are prohibitively expensive. Wastes can also be blended with coal before combustion in a conventional boiler, but the waste materials often segregate during storage and handling, so as to cause slugs of waste to enter the boiler. Normally, the heat content and combustion characteristics of waste are very different from coal. If wastes enter the boiler as slugs, the operators must deal with a high variable feed and boiler efficiency may drop. Also, wastes are typically more difficult to handle than coal, potentially causing feed shoots and vents to plug. In sum, these approaches to using waste as fuel have been unsuccessful in that the particles are not uniformly agglomerated.
Numerous processes have been proposed and implemented in the past for agglomerating particles. Most forms of agglomeration methods use either an organic binder such as lignosulfonate, petroleum pitch, latex or polymers, or an inorganic binder such as cement or bentonite. Binder choice depends principally on the cost of the binder and product quality required.
U.S. Pat. No. 44,994 to Cornell, issued over a century ago, teaches that coal dust can be pelletized by saturating it with a solution of starch, pressing it, or otherwise forming it into blocks or lumps, and drying it in the sun or by other suitable means. When these starch-based binders are used, the resulting green pellets must be dried to achieve acceptable fuel performance and reduce transportation costs. Also, starches and sulfates have no apparent ability to completely fuse the coal fines. Moreover, when rewetted, the bond weakens. Thus, pellets made with starch and sulphate binders are neither strong nor water proof. Sulfates also add sulfur to the coal which produces undesirable sulfur oxides and stack gases, which is direct noncompliance with the clean air regulations.
U.S. Pat. No. 852,025 to Mashek discloses preparing coal for briquetting by drying and heating it, mixing an asphaltic binder material, then heating, cooling, and compacting the mixture. More recently, U.S. Pat. No. 5,752,993 to Eatough discloses a binder composition made up of tar, acid, a polymeric binder, water and, if necessary, a surfactant to aid in wetting the carbonaceous material. These asphaltic and tar binder compositions are well known in the art. However, they do not sufficiently prevent the bound material from absorbing water and they are not suitable for industrial use due to there soft and xe2x80x9cgummyxe2x80x9d characteristics. These binders produce a product that fouls the feed lines to furnaces by clogging the inlets. Neither can they be transported or stored without absorbing water and either degrading or decreasing in BTU content.
Many other natural and synthetic particles have been utilized as binders for coal fines. U.S. Pat. No. 5,244,473 to Sardessai discloses a binder for coal fines made from a phenolaldehyde resin mixed with a polyisocyanate in the presence of a catalyst. U.S. Pat. No. 5,089,540 to Armbruster discloses a binder for foundry molds made from an extra cured alkaline phenolic resin, which can be enhanced by conditioning the reclaimed sand with a solution containing an amine and a saline. Likewise, U.S. Pat. No. 5,487,764 to Ford discloses the use of a binder composition made up of a styrene in a hygroscopic solvent (methyl ethyl ketone), polyvinyl acetate and water. Regrettably these prior art binders are derived from useful and often expensive raw materials such as natural and synthetic polymer, thereby adding significantly to the overall cost of the briquette and making there use cost prohibitive.
The use of such binders requires water. Unfortunately, the heating value of coal decreases as moisture content increases. Moreover, large amounts of water are associated with the fine coal either because it is being recovered from black water ponds or because the fines are slurried with the binder to achieve the desired coating. Regardless, water in the final product is undesirable as it is useless weight, increasing transportation costs and, as a result, decreasing the BTU content per ton. As a result, the prior art has failed to produce synthetic fuels that have sufficient heating value.
Therefore, a need has remained for an inexpensive, yet reliable, coal binder that, when used to produce a fuel product, produces a strong, weather resistant, environmentally compliant fuel product.
The government has provided yet another incentive: a tax credit to those who create synthetic fuels. To qualify for this credit fuels must undergo a xe2x80x9csignificant chemical change.xe2x80x9d The change is measured by comparing the synthetic fuel product to ingredients used to make it. Laboratory measurements of the feed stock coal, binders, additives and/or supplements are composited and compared to the synthetic fuel to verify that the chemistry of the synthetic fuel cannot be predicted from the ingredients. If the chemistry of the product is different than a mere mixture of the ingredients and the differences are statistically significant, the fuel may be deemed qualified. With the above binder shortcomings in mind it is apparent there is still need for improved binders and briquetting processes.
In accordance with the invention binder compositions are provided comprising a distillable petroleum hydrocarbon emulsified with a surfactant and water. In one embodiment, the binder composition includes the addition of a base. The petroleum hydrocarbons are emulsified with a surfactant and water by conventional means. In a particular embodiment of the invention the binder is emulsified in a colloid mill.
In one specific embodiment, a method is provided for making a binder composition for converting carbonaceous materials into fuel. The method includes blending a distillable petroleum hydrocarbon with water and a surfactant.
In another aspect a fuel product is provided which includes the reaction product of fine carbonaceous materials and binder composition including a petroleum hydrocarbon emulsified with a surfactant and water in an amount necessary to increase the hydrophobic characteristics of the fine carbonaceous materials.
In one aspect a method for using the binder composition to bind fine carbonaceous material is disclosed wherein the fine carbonaceous materials are exposed to the binder composition to produce fuel. In one embodiment the binder composition is present in an amount between about 1.5 percent and about 4.0 percent of the total weight. In another embodiment the binder composition is used as a vehicle for the addition of chemical additives. These additives are typically added to reduce ashing. In still another embodiment the fuel is solidified by conventional means into a briquette or pellet.
One object of the invention is to provide an inexpensive coal binder that can be used to reliable produce a strong, weather-resistant and environmentally compliant fuel product from coal waste.
Other objects and further benefits of the present invention will become apparent to persons of ordinary skill in the art from the following written description and accompanying Figures.